In forming slip cast articles, I have long worked with stabilized silicon slips where water is a vehicle for forming the slip. The stabilized slips generally have a pH in the range from 6.5 to 7.9 and exhibit a minimum viscosity and result in the production of a slip cast article having the maximum density. The making and using of such silicon slips are disclosed more thoroughly in U.S. patent application Ser. No. 415,898 filed Nov. 14, 1973, now abandoned, and assigned to the same assignee as this application. This prior application is hereby incorporated by reference. The use of such slips in slip casting operations results in the production of a final article which is of uniform density throughout its entire extent.
I have been endeavoring to develop articles which would have zones of cellular construction, such zones being connected in a homogeneous and uniform manner to a zone of different cellular density or of noncellular construction. Such an article, for example, would be of value in forming a bullet-like structure which forms a portion of a flow path for a gas turbine engine in which all of the principal elements are formed from ceramic material. This bullet-like structure would have an outer skin of noncellular construction of high and uniform density connected directly to a cellular zone of low density which would provide strength and rigidity for the outer skin.
I have now developed a method by which slip cast articles can be made from slips containing water as the slip vehicle and an oxidizable metal as a casting material, these articles having at least one zone of cellular construction therein. My method permits the manufacture of articles having zones of different cellular density, articles which have gradual but changing zones of different cellular density, and articles having intermixed zones of cellular and noncellular construction.